Examples of this kind of hollow member include a housing for an incore monitor (ICM) which serves to monitor the neutron flux generating in the RPV, and a housing for a control-rod drive (CRD) which serves to drive the control rod.
The hollow member, e.g. the ICM housing, extends through a wall of the RPV into the coolant while it is welded to the wall of the RPV through a cladding weld formed on an inner surface of the RPV wall. Such ICM housing is made of TYPE 304 stainless steel. In general, a welding residual stress exists in the weld as a result of the welding heat input. Under the presence of the welding residual stress, corrosion proceeds markedly at the weld of the ICM housing in the coolant, resulting in cracking. This phenomenon is referred to as the stress corrosion cracking. Upon the occurrence of the stress corrosion cracking in the weld of the ICM housing, there is the possibility that the coolant leaks out of the RPV.
Once the stress corrosion cracking has occurred, repair may be conducted by a known method in which a shielding member is welded to the hollow member to surround the stress corrosion cracked portion as disclosed in JP-U-56-82696. On the contrary, as disclosed in JP-A-2-128195, an ICM housing lower half including a part thereof in which the stress corrosion cracking has occurred is cut and removed to replace it with a new ICM housing half welded to the remaining housing half.
However, these repairing methods will make another new weld which presents a danger of stress corrosion cracking.